Automated bulk optical processing equipment can perform a variety of tasks such as, for example, inspecting or sorting bulk articles including raw or processed fruit, vegetables, wood chips, recycled plastics and other similar products. The articles may be characterized according to size, color, shape or other qualities. Modern bulk optical processing equipment can rapidly separate very large quantities of articles into numerous categories.
Such equipment typically includes a conveyor system that moves the articles past an inspection station where cameras or other detection devices examine the articles as they pass by a scan line. The inspection station sends signals to a sorting or treatment station where the articles are sorted or otherwise treated by category. For example, defective or foreign articles may be removed from the flow of articles carried by the conveyor system.
Rapid inspection or sorting of large quantities of articles typically requires high-speed conveyor systems such as, for example, conveyor belts with widths of 2-6 ft (0.6-1.8 m) and that carry articles at speeds of over 10 ft/sec (3 m/sec). A problem with conveyor systems driven at such speeds is that many articles are relatively unstable on the belts and tend to roll, tumble, bounce and collide with one another. Unstable articles carried by a high-speed conveyor system are difficult to inspect, sort or otherwise process for at least two reasons.
First, automated bulk optical processing equipment includes cameras or other optical detectors that optically determine selected characteristics of the articles (e.g., size, color or shape). The rolling, tumbling or bouncing of an article typically diminishes the clarity with which an image of the article is generated, thereby decreasing the accuracy and reliability of the optical information about the article. As extreme examples, rolling could cause a cubic article to appear round or an article with regions of two different colors to be of a single mixed color.
Second, unstable articles moving on a conveyor belt can move laterally across the belt or along the belt in its direction of travel. Lateral movement of the articles is undesirable because it misaligns the articles as they pass from the inspection station to the processing station, thereby resulting in incorrect processing. Similarly, articles that move along the belt in its direction of travel have different effective speeds along the belt and may be temporally misaligned for subsequent processing operations.
Some articles have increased susceptibility to unstable motion on a conveyor, such as light-weight articles and articles of low and non-uniform density. Examples of such articles include tobacco products such as stripped-leaf tobacco or laminae, ground tobacco stems, and re-claim. Other examples include wood chips. Yet other such light-weight articles might include debris such as, for example, feathers, paper or plastic wrappers or string that may incidentally be included within the acceptable articles. As a consequence, these types of articles are difficult to inspect and sort accurately at high speeds.
One attempt to solve such instability problems can be seen in U.S. Pat. No. 5,297,667 for a System For Stabilizing Articles On Conveyors, assigned to the assignee of this patent application. This device uses a hood located just above the belt to create a flow of gas (e.g., air) projected along the conveyor belt in a direction generally parallel to that in which the articles are carried by the belt. The air flow has a velocity substantially the same as that above the belt to reduce aerodynamic resistance that would otherwise bear against the articles causing them to become unstable. Since this resistance is reduced, the articles carried by the belt are relatively stable. The articles are accelerated by and propelled from the belt in-air along a known and predictable trajectory to a sorting or processing station. The successful operation of the sorter or processor depends on the fact that the products are propelled along the known trajectory. Thus, the processor notes the exact position of the articles as they pass by and can separate defective or undesirable articles from the volume of acceptable articles. This type of system has been successful for articles having a relatively high mass. Articles with high mass are able to maintain their velocity in-air as they are projected from the belt and continue along their predicted trajectory.
Another attempt to stabilize articles as they are moved along a conveyor belt is the use of a second counter-rotating conveyor belt located above and close to the conveyor belt on which the articles are positioned. Instead of blowing air through a hood that encloses the conveyor belt, the second counter-rotating conveyor belt creates a flow of air in a direction generally parallel to the direction of travel of the articles. The flow of air generated by the second counter-rotating conveyor belt has a velocity about the same as the article-conveying belt to reduce any aerodynamic resistance that would otherwise bear against the articles. One example of such a system is the Tobacco Scan 6000 manufactured by Elbicon located near Brussels, Belgium.
However, these systems are inadequate for very light articles such as the tobacco products described above, wood chips, light-weight debris or articles having a weight of between 1.5-5 pounds per cubic foot. Light-weight articles become unstable after they leave the belt and travel along an unknown trajectory. This happens because air flow becomes unstable after it leaves the belt. The air profile separates into a random flow pattern. A portion of the air flows downward while another portion flows straight. Yet other parts of the air may flow upward or in a direction transverse to the direction of travel of the belt. The light-weight articles do not have enough mass to continue along a predicted trajectory. They lose velocity and are drawn into a random air flow pattern. The positions of the articles cannot be predicted at a specific time. This makes accurate processing of the articles difficult and impractical.
Another problem with existing systems is inadequate illumination of the articles. In current systems, an illumination station includes light tubes to illuminate the articles. Clear plastic covers are placed over the light tubes to protect them from the articles as they are projected past the illumination station. This increases the distance between the light tubes and the articles. The distant placement of the light tubes from the articles may cause shadows to appear. The camera may improperly view the shadow as another article, thereby resulting in a miscalculation and improper processing. The light tubes cannot be placed directly over the scan line because they would block the camera's view of the articles. It is desirable to place the light tubes as close to or as collinear with the camera scan line as possible to reduce shadows.